This invention relates generally to micromechanical systems, and more particularly to a micromirror device.
There are a variety of different types of micromechanical devices, including micro-motors, micro-gears, and micromechanical deformable mirror devices (DMD""s). Micromechanical DMD""s contain an activation or addressing electrode, a support post or posts, underneath a hinge or hinges, which in turn supports a deflection element suspended over the electrode. The DMD""s are primarily used in the direction of light in optical systems, with a mirrored deflection element. The operation of such devices involves activating the electrode, which builds up electrostatic charge in the gap between electrode and deflection element. The deflection element then flexes on its hinge or hinges and moves towards the electrode. When the charge is removed, the deflection element returns to its undeflected position. MEM micromirrors are used to build digital micromirror display (DMD) devices where the mirrors rotate about a single axis by an electrostatic drive.
In recent years, optical fibers have come into widespread use in a wide variety of applications, in which optical signals are transmitted along such fibers and are switched from one fiber to another by means of an optical switch. An optical switch and micromirror used therein is described in U.S. Pat. No. 6,295,154, issued on Sep. 25, 2001 to Laor, et al., incorporated herein by reference. The micromirror includes two axes of motion and is driven magnetically, e.g., by coils disposed under magnets on the micromirror. The micromirror is made from a single piece of crystal material such as silicon and has three portions connected by two sets of hinges, with an inner portion forming the mirror. One of the hinge pairs, one hinge on each of two opposite sides of the mirror portion, ties the mirror portion and the middle gimbals portion, which surrounds the mirror portion. This allows the mirror portion to rotate about the gimbals portion, providing the first axis of rotation. The second set of hinges ties the gimbals portion and the frame portion, one hinge on each of two opposite sides on a line disposed, e.g., 90 degrees relative to a line drawn through the first set of hinges. This allows the gimbals portion, which carries the mirror, to rotate about the frame portion, providing a second axis of rotation.
In the micromirror device disclosed in U.S. Pat. No. 6,295,154, because there are two axes of rotation, the micromirror may be deflected +/xe2x88x92 around 8 degrees, in both directions from the surface normal in a plurality of positions, and is therefore sometimes referred to as an analog micromirror device. The analog micromirror device mirror portion can move to a nearly infinite number of positions within the +/xe2x88x928 degrees in both axes, and is limited only by the resolution of the electronics that drive the coils.
Embodiments of the present invention achieve technical advantages by disclosing a micromirror device having around one-tenth the thickness of prior art micromirror devices, achieving a higher resonant frequency, in the order of thousands of Hertz. The decreased thickness is possible due to the use of a plurality of trusses disposed beneath at least a mirror portion of the micromirror device. The micromirror device may be used in optical switching systems, increasing the switching speed of optical switches, devices and networks.
In one embodiment, disclosed is a micromirror device, comprising an outer frame portion, a rotational gimbal portion hinged to the frame portion and moveable relative to the frame portion about a first axis, and an inner rotational mirror portion having a reflective upper face surface hinged to the gimbal portion for movement of the mirror portion relative to the gimbal portion about a second axis. A plurality of truss members are disposed beneath at least the inner rotational mirror portion.
In another embodiment, a micromirror device is disclosed, comprising an outer frame portion, a rotational gimbal portion hinged to the frame portion and moveable relative to the frame portion about a first axis, and an inner rotational mirror portion having a reflective upper face surface hinged to the gimbal portion for movement of the mirror portion relative to the gimbal portion about a second axis. A plurality of truss members are disposed beneath the inner rotational mirror portion and the gimbal portion, wherein at least the gimbal portion and mirror portion are formed from a single piece of material.
Further disclosed is a method of manufacturing a micromirror device, the method comprising providing a silicon on insulator (SOI) wafer having a first layer bonded to a second layer, a thin oxide layer being disposed between the first and second layers, wherein the second layer is thicker than the first layer. The method includes removing a portion of the second layer to define a truss member height in the second layer, and patterning and etching the truss member height defined areas of the second layer to form a plurality of truss members. The first layer is patterned and etched to form a frame portion, a gimbal portion disposed within the frame portion, and a mirror portion disposed within the gimbal portion.
Advantages of embodiments of the present invention include reducing the mass of the mirror portion and gimbal portion of a micromirror device, which increases the resonant frequency, allowing the micromirror device to move faster. Larger micromirror devices can be manufactured, having higher resonant frequencies. Furthermore, standard SOI wafers may be used to manufacture the micromirror device, reducing cost and avoiding the manufacture of custom SOI wafers.